Relationship between the concentration of bacteria in saliva and the colonization of teeth in humans.

The relationship between the salivary concentration of bacteria and their number that can be recovered from tooth surfaces has been studied in 12 human subjects. The mean salivary concentration of naturally occurring Steptococcus mutans and lactobacilli, determined on selective media, was 3.7 x 10(5) and 3.8 x 10(5) colony-forming units (CFU) per ml, respectively. In subjects with salivary concentrations of S. mutans of about 10(4) CFU/ml or less or about 10(5) CFU/ml or less of lactobacilli, these organisms could not be isolated from cleaned teeth after 2 to 3 h of oral exposure. In experiments with streptomycin-labeled S. sanguis cells held in the mouth for 15 min, the minimal salivary concentration required for their recovery from the teeth was about 10(3) CFU/ml. Both S. mutans and lactobacilli were found to be highly localized on teeth. This evidence suggests that the concentrations of S. mutans and lactobacilli generally present in saliva are insufficient for the initiation of their firm attachment to relatively nonretentive tooth surfaces. The low efficiency of their intraoral spread, as suggested by their highly localized distribution on teeth, or of their transmission between subjects may be essentially due to the interrelated factors bacterial affinity and number of colony-forming units available for attachment.